Historically, aircraft internal combustion engines have utilized conventional magnetos to provide the ignition spark needed to ignite the combustible mixture within the combustion chamber of the engine. Magnetos have usually been provided in pairs in order to satisfy the desire for redundancy in the ignition system such that in the event of the failure of one magneto, the engine will continue to run, albeit at somewhat reduced efficiency on the remaining magneto. The magnetos are usually mounted on an accessory case positioned at or near the rear of the engine away from the propeller and are secured thereto on appropriate mounting pads which accommodate suitable fasteners to adjustably secure the magneto in a predetermined position on the pad. The magneto is driven by gears contained within the accessory case usually associated with the crankshaft and/or cam shaft and thus, the magneto is driven to provide ignition spark at the appropriate time on the compression stroke of each cylinder.
The magneto usually includes an appropriate coil and condenser defining a tank circuit and houses the coil within the magneto body together with the appropriate mechanical breaker system for distributing the spark to the appropriate cylinder in the proper time sequence.
It is further well known in the field of aircraft engine ignition systems that some means must be provided in order to retard the spark during the starting phases of engine operation and to automatically advance the spark once the engine has started to run. This change in spark timing is normally achieved by the use of an impulse coupler which is positioned on the magneto drive shaft and tends to retard the spark during the starting phase and by means of centrifugal force, advance the spark to a predetermined timing degree once the engine is running under its own power and not relying on the starter motor to provide rotational force.
Thus, it may be seen that conventional magnetos include a combination of features which are necessary to the proper operation of the engine depending upon whether the engine is in the starting phase or the running phase.
In recent years, automotive ignition systems have advanced to a breakerless arrangement wherein electronic devices provide the proper generation, timing and delivery of the electrical energy to the spark plugs without the need for the troublesome breaker points of the conventional ignition system. These devices have not, however, found their way in any significant numbers into the aircraft engine field and it is to this environment that applicant's invention is directed.